Liu Yang, Tang Feng, Wang Xiangzhao, Peng Changzhe, Li Peng
Appl Opt. 2022 Feb 20;61(6):1464-1474. doi: 10.1364/AO.448794.
Ronchi shearing interferometry is a promising technique for in situ wavefront aberration measurement of the projection lens in advanced photolithography systems. The Van Cittert-Zernike theorem has been used to analyze the interference signal of a Ronchi shearing interferometer in the effective interference area (overlapping area of the ±1st diffraction orders produced by the image grating). However, the applicability of this theorem has not been systematically studied. In this work, the analytical expression of the Ronchigram in this area is derived based on the theory of scalar diffraction and incoherent imaging. The results show that only the object and image grating with infinite diffraction orders can fully satisfy the Van Cittert-Zernike theorem. In the finite diffraction orders case, the theorem can be considered approximately applicable in the overlapping area of the ±3rd diffraction orders produced by the image grating. The applicable area extends to the overlapping area of the ±2nd diffraction orders under a shear ratio of less than 1%, which accounts for 97% of the effective interference area. The theoretical analysis has been verified by simulation and fundamental experiments.
龙奇切变干涉测量法是一种很有前景的技术，可用于先进光刻系统中投影透镜的原位波前像差测量。范西特 - 泽尼克定理已被用于分析龙奇切变干涉仪在有效干涉区域（图像光栅产生的±1级衍射级的重叠区域）内的干涉信号。然而，该定理的适用性尚未得到系统研究。在这项工作中，基于标量衍射理论和非相干成像理论，推导了该区域内干涉图的解析表达式。结果表明，只有具有无限衍射级的物光栅和像光栅才能完全满足范西特 - 泽尼克定理。在有限衍射级的情况下，该定理在图像光栅产生的±3级衍射级的重叠区域可近似适用。在剪切比小于1%的情况下，适用区域扩展到±2级衍射级的重叠区域，该区域占有效干涉区域的97%。理论分析已通过模拟和基础实验得到验证。
